1. Field of the Invention
The present invention relates to a gas friction pump including a housing having a suction opening and an exhaust opening, main rotor and stator components arranged in the housing and cooperating with each other for delivering gases and for producing a pressure difference, and a shaft arranged in the housing for supporting the main rotor components.
2. Description of the Prior Art
It is known to deliver gases with gas friction pump of different types. Their operation is based on transmission of pulses of movable wall to gas particles. In this way gas flow in a desired direction is obtained. Gas friction pumps, which operate in a pressure region in which the mean free displacement path of gas molecules is large in comparison with geometrical dimensions of the pump, i.e., which operate in a molecular flow region, are called molecular pump.
The first gas friction pumps of this type were conceived by Gaede (w. Gaede, Ann. Phys. 41 (1913), 337). The gas friction pumps were subsequently modified, with retention of the basic principle of these pumps, by Siegbahn (M. Siegbahn, Arch. Math. Astr. Fys. 30B (1943), Holweck (F. Holweck, Comptes Reduc. Acad. Science 177, 1923, p. 43) and Becker (W. Becker, Vacuum Technik (Vacuum Technology) Sep. 10, 1966). The pump, which is modified by Becker, is known as turbomolecular pump. The turbomolecular pumps found wide application in industry and science. Therefore, they would be used as an example for purposes of explanation of the present invention.
Below the drawbacks of conventional turbomolecular pumps will be described, together with explanation how the present invention permits to eliminate these drawbacks. It is to be noted that the present invention can be used not only in turbomolecular pumps but also in other types of gas friction pumps.
The suction capacity of a turbomolecular pump essentially depends on the inlet cross-section of the suction flange, mean circumferential speed of the rotor vane rim and the structure of the rotor vane adjacent to the pumping-out chamber. In addition, the suction capacity depends on the inner structure of the pump, on the gradation of pressure ratio and suction capacity between separate stages, and last but not least, on those portion of the pump or combination of pumps which is discharged against the atmospheric pressure.
The above-discussed parameters can be so optimized and the rotational speed can be so increase, within the frame of technical possibilities, that the largest portion of molecules, which are found on the rotor vane rim, e.g., can be pumped out. However, those molecules do not contain all of the molecules which are found on the inlet cross-section of the suction flange. A large portion of this cross-sectional surface is formed by the rotor end surface that does not have a gas delivery structure. Even when the rotor vane rim is increased, at the costs of reducing the rotor end surface, the suction capacity is still limited by the cross-section of the suction flange. The amount of pumped-out molecules cannot be larger than the amount of molecules to be found on the gas delivery structure of the inlet stage.
Accordingly, an object of the invention is to provide a gas friction pump having a noticeably increased suction capacity in comparison with conventional gas friction pumps at the same cross-section of the suction flange.
This and other objects of the present invention, which will become apparent hereinafter are achieved by providing an auxiliary pumping unit provided at a side of the suction opening and having a gas delivery structure that provides for gas delivery in a radial direction, with the auxiliary pumping unit being formed of at least one stage and having auxiliary rotor and stator components, with the auxiliary rotor components being supported on the shaft which supports the main rotor components.
Advantageously, the auxiliary pumping unit, which can be formed of one or several stages, has a gas delivery structure such that in addition to the gas delivery in the axial direction, gas delivery in the radial direction is provided for. With this auxiliary pumping unit, the suction capacity of the pump is not limited any more by the cross-section of the suction flange. The entire gas delivery structure, on which the gas molecules accumulate, is increased, as a result of providing of the auxiliary pumping unit. Moreover, this surface is further provided with a radial gas delivery component.
The biggest effect of providing an auxiliary pumping unit is achieved when the auxiliary pumping unit is arranged completely or partially above the pump housing. However, for constructional reasons, it may be necessary to arranged the auxiliary pumping unit completely or partially inside the pump housing. Even when the auxiliary pumping unit is arranged entirely in the pump housing, certain advantages are achieved, in comparison with the conventional gas friction pumps, as a result of the auxiliary pumping unit being provided with radial gas delivery components.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to is construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.